A diode package name encodes two facts: how the part mounts and which size class it belongs to. The common diode package types split into three groups — through-hole DO outlines, surface-mount SOD small-signal packages, and the SMA/SMB/SMC rectifier family (JEDEC’s DO-214). Your choice sets board area, assembly method, and thermal ceiling. It does not, by itself, set current rating — copper does, and this guide shows why with manufacturer data.
| Key takeawaysDO = Diode Outline (through-hole, mostly axial); SOD = Small Outline Diode (small-signal SMD); SMA/SMB/SMC are trade names for JEDEC DO-214AC / DO-214AA / DO-214AB.In the DO-214 family the letters are size steps only: SMA is smallest, SMC largest — SMA → SMB → SMC.In the SOD family a higher number is generally smaller: SOD-123 (largest) → SOD-323 → SOD-523 → SOD-923.A bigger package raises the thermal ceiling, but the real current limit follows PCB copper area — the same SMC runs ~47 °C/W on 8×8 mm copper versus ~90 °C/W on minimum pads (Vishay).Flat-lead and low-profile variants (SOD-123F, SMF = DO-219AB, SlimSMA = DO-221AC) trade a little area or height for better thermal or profile.Land patterns are per datasheet, not universal — two parts sharing a package name can want slightly different footprints. |
How diode package names actually decode
DO stands for Diode Outline, a JEDEC registration series. Most through-hole diodes are axial two-terminal parts in the DO-204 sub-family — for example DO-35 is also DO-204AH and DO-41 is also DO-204AL, per the manufacturer datasheets that carry both designations. Small-signal DO parts are usually glass-bodied; rectifiers are molded plastic. Polarity is marked with a cathode band.
SOD stands for Small Outline Diode — a flat, two-lead surface-mount body. The numbering is counter-intuitive: within the common series a larger number is a smaller part, so SOD-123 is the largest and SOD-923 the smallest, as documented by Diodes Incorporated’s package outlines. A suffix of F or FL means flat leads instead of the default gull-wing (SOD-323 is gull-wing; SOD-323F is flat-lead). Some carry JEITA cross-names — SOD-323 is also SC-76.
SMA, SMB, and SMC are industry trade names, not JEDEC names. Their formal designations are DO-214AC (SMA), DO-214AA (SMB), and DO-214AB (SMC), a family JEDEC first registered in 1994. The letters are size increments: SMA smallest, SMC largest. Glass-passivated versions carry the DO-215 designation (SMBG = DO-215AA, SMCG = DO-215AB), and low-profile or flat-lead cousins include SMF (DO-219AB), MicroSMF (DO-219AC), SMP (DO-220AA), and SlimSMA (DO-221AC), all listed in Vishay’s AEC-qualified package overview.
MELF (metal electrode leadless face) is the cylindrical glass alternative. Its smaller version, MiniMELF, is the same outline as SOD-80 and DO-213AA; the full-size MELF is DO-213AB. Every package here is two-terminal — the difference that follows is size, mounting, and how much heat the board can pull out.
Through-hole DO packages: still the right call sometimes
Through-hole axial diodes are bulky and slower to place, but they tolerate shock, vibration, and hand assembly better than any SMD, which keeps them in power supplies, socketed prototypes, and high-surge inputs. Dimensions below are from manufacturer datasheets.
[IMAGE 1: Axial through-hole diodes DO-35, DO-15, DO-41, DO-201AD shown to scale with a surface-mount SMA for size reference — alt: “Diode package types compared: through-hole DO-35, DO-15, DO-41 and DO-201AD axial bodies next to a surface-mount SMA”]
| Package | JEDEC alt. name | Body size (L × dia, mm) | Typical rating | Example parts |
| DO-35 | DO-204AH | ~3.6 × 1.8 (glass) | ~0.5 W, ≤ 200 mA signal | 1N4148, 1N914 |
| DO-15 | DO-204AC | ~5.8 × 2.7 | ~1 A rectifier | 1N5391–1N5399, RL207 |
| DO-41 | DO-204AL | 4.06–5.21 × 2.00–2.72 | ~1 A, ≤ 1000 V | 1N4001–1N4007, 1N5819 |
| DO-201AD | — | ~9.5 × 5.2 | ~3 A rectifier / TVS | 1N5400–1N5408, 1.5KE TVS |
For the workhorse DO-41, the onsemi/Diodes 1N4001–1N4007 datasheet specifies a body length of 4.06–5.21 mm, a body diameter of 2.00–2.72 mm, and lead diameter 0.71–0.864 mm — a 1 A rectifier available from 50 V to 1000 V. The signal-class DO-35 glass body (1N4148) is roughly 3.6 × 1.8 mm and rated about 0.5 W. Reach for through-hole only when you genuinely need leaded robustness or high single-pulse surge, since DO-201AD parts host 1500 W TVS devices like the 1.5KE series.
SOD packages: small-signal surface mount
SOD is where switching diodes, small Schottkys, Zeners, and ESD/TVS parts live on modern boards. These are low-current bodies chosen for area, not power.
| Package | Alias | Body size (L × W × H, mm) | Land area | Example parts |
| SOD-123 | SOD-123F = DO-219AA (flat lead) | ~3.7 × 1.8 × 1.35 | — | 1N4148W, MBR0520 |
| SOD-323 | SC-76 (JEITA) | ~2.5 × 1.25 × 1.0 | — | 1N4148WS, BAS316 |
| SOD-523 | EMD2 (ROHM) | 1.65 × 0.80 × 0.60 | 2.58 mm² | RB751S40, BAS516 |
| SOD-923 | — | ~1.0 × 0.5 | — | ultra-compact ESD diodes |
| SOD-882 | leadless, 0402 footprint | ~1.0 × 0.6 | — | TVS/ESD arrays (e.g., SP1003) |
The SOD-523 body is tightly specified — 1.65 × 0.80 × 0.60 mm with a 2.58 mm² land (2.15 × 1.20 mm) and 1.40 mm pad pitch, per onsemi’s RB751S40 and NXP’s SOD523 package drawing. SOD-123 is the largest of the group and the easiest to hand-rework; its flat-lead sibling SOD-123F shares dimensions with DO-219AA and pulls heat through the board better, which is why thermally-stressed Schottkys use it. Default SOD leads are gull-wing; flat-lead (F/FL) versions give a lower profile and a shorter thermal path at the cost of hand-soldering ease.
SMA, SMB, SMC: the DO-214 rectifier and TVS family
These three are the surface-mount rectifier and transient-suppressor workhorses. Body dimensions below are read from Vishay’s DO-214 outline drawings.
[IMAGE 2: SMA (DO-214AC), SMB (DO-214AA) and SMC (DO-214AB) gull-wing bodies to scale with cathode band and recommended land patterns — alt: “SMA, SMB and SMC diode packages (DO-214AC, DO-214AA, DO-214AB) shown to scale with cathode bands and PCB land patterns”]
| Trade name | JEDEC | Body (L × W, mm) | Height (mm) | Length across leads | Typical current | Example parts |
| SMA | DO-214AC | ~4.3 × 2.6 | ≤ 2.30 | ≤ 5.28 mm | ~1–2 A | M7, SS14, US2A, SMAJ5.0A |
| SMB | DO-214AA | ~4.6–5.0 × 3.9 | ≤ 2.40 | ~5.6 mm | ~2–3 A | SS24, SK24, P6SMB TVS |
| SMC | DO-214AB | ~6.9 × 5.9 | ~2.6 | 7.75–8.13 mm | ~3 A and up | SS34, SK34, P6SMC TVS |
Vishay’s DO-214AC drawing gives the SMA a body height of 2.30 mm max and an overall length across the leads of 5.28 mm max; the DO-214AB drawing gives the SMC an overall length of 7.75–8.13 mm and a seated height near 2.62 mm, using about 50.6 mm² of board. The size letters map to current class only loosely: the classic SS14 / SS24 / SS34 Schottky trio (and SK24 / SK34) differ mainly in current, sharing the same die concept across SMA/SMB/SMC. When you need SMA area with a lower profile or flat leads, the SMF (DO-219AB) and SlimSMA (DO-221AC) outlines are pin-usable alternatives.
The package does not set the current — copper does
This is the point competitor pages skip. A package name sets a thermal ceiling, but the current a diode can actually carry depends on how much copper you give it, because that copper is most of the junction-to-ambient path.
Vishay’s data for the SMC makes it concrete: junction-to-case resistance is about 10–16 °C/W, but junction-to-ambient swings from roughly 47–55 °C/W on two 8 × 8 mm copper pads to about 90 °C/W on minimum pads — nearly double the thermal resistance for the same package. Nexperia’s SOD-323 shows the same effect at small-signal scale: θJA falls from about 450 K/W on a standard footprint to about 210 K/W once you add a 1 cm² cathode copper area, with θJC around 90 K/W.
The design consequence is a short calculation, not a lookup. Junction temperature rise is ΔT = P × θJA, where P ≈ VF × Iavg. A diode dropping 0.5 V at 1 A dissipates 0.5 W; on an SMC at 55 °C/W that is a ~28 °C rise, comfortably under the 150 °C junction limit — but on minimum copper at 90 °C/W the same part rises ~45 °C, and with switching losses added the margin erodes fast. Size the copper to your target junction temperature; don’t trust the “SMA = 1 A” shorthand.
Footprints, standards, and compliance
Treat the package name as a shelf, not a land pattern. The four-letter body fixes the outline, but pad geometry, solder-fillet room, and thermal relief still come from the specific datasheet — two “SMB” parts from different vendors can want slightly different footprints, and MELF’s cylindrical body needs its own curved-pad land. JEDEC registers the outlines behind all of this (the DO-204, DO-213, DO-214, DO-215, DO-219, DO-220, and DO-221 series).
For automotive work, the relevant qualification is AEC-Q101 — “Failure Mechanism Based Stress Test Qualification for Discrete Semiconductors,” Rev E dated March 1, 2021 — which covers diodes and transistors, molded or glass, over a minimum −40 °C to +125 °C operating range (LEDs −40 °C to +85 °C). Plastic SMD bodies also carry a moisture-sensitivity level (JEDEC J-STD-020) that dictates bake-and-reflow handling, while hermetic glass MELF and axial parts are not moisture-sensitive. Confirm RoHS/REACH status from the ordering suffix — for example the “-LF” lead-free suffix on 1N400x parts.
Worked example: a 2 A buck freewheeling diode
Say you need a Schottky freewheeling diode for a 2 A buck output and want surface mount. Start at the smallest plausible body — SMB (DO-214AA) with an SS24 (2 A, 40 V). Check forward drop at 2 A from the datasheet (~0.5 V), so P ≈ 1.0 W. On an SMB with adequate copper (θJA in the ~55–75 °C/W range), ΔT is ~55–75 °C, keeping the junction under 150 °C at room ambient — but at 85 °C ambient the margin is thin, so either pour more copper, step up to SMC (SS34) for a lower θJA and more pad area, or accept a lower current. That progression — start small, verify junction temperature against real copper, step up only if the thermal math fails — is the whole selection method.
Frequently asked questions
What is the difference between SMA, SMB, and SMC?
They are size steps in JEDEC’s DO-214 family: SMA is DO-214AC (smallest), SMB is DO-214AA (middle), and SMC is DO-214AB (largest). Larger bodies give more copper-attach area and a higher thermal ceiling, so they host higher-current rectifiers and higher-power TVS parts, but the letter itself is size, not a fixed current rating.
What does DO stand for in diode packages?
DO stands for Diode Outline, a JEDEC package-registration series. Most through-hole diodes are axial parts in the DO-204 sub-family — DO-35 (DO-204AH) for small-signal glass parts and DO-41 (DO-204AL) for 1 A rectifiers such as the 1N4001–1N4007.
What is the SMD equivalent of a DO-41 diode?
For a 1 A rectifier, the surface-mount equivalent is usually SMA (DO-214AC) — the M7 is the SMA version of the through-hole 1N4007. If the design needs more thermal headroom, SMB (DO-214AA) is the next step up.
Is SOD-123 or SOD-323 bigger?
SOD-123 is larger. In the SOD series a higher number is generally a smaller body, so SOD-123 (~3.7 × 1.8 mm) is bigger than SOD-323 (~2.5 × 1.25 mm), which is in turn bigger than SOD-523 (1.65 × 0.80 mm).
Does a bigger diode package mean higher current?
Not directly. A bigger package raises the thermal ceiling, but the real current limit tracks PCB copper area — Vishay’s SMC runs about 47–55 °C/W junction-to-ambient on 8 × 8 mm copper versus ~90 °C/W on minimum pads. Size copper to hold the junction under its limit rather than reading current off the package name.
What package is a 1N4007 in?
The through-hole 1N4007 is a DO-41 (DO-204AL) axial part rated 1 A, 1000 V. Its surface-mount counterpart is the M7 in an SMA (DO-214AC) body.
The decision
Decode first, then size to heat. If a schematic shows an unfamiliar name, map it: DO-xx is through-hole, SOD-xxx is small-signal SMD, and SMA/SMB/SMC are DO-214AC/AA/AB rectifier bodies. To choose, start at the smallest package that clears your voltage and area constraints, then run ΔT = VF × I × θJA against the copper you can actually provide and keep the junction below 150 °C — or 125 °C for AEC-Q101 automotive parts. Step up a size, add copper, or move to a flat-lead variant only when that math fails. The package name gets you to the right shelf; the thermal calculation and the specific datasheet’s land pattern get you a board that survives.
